Final answer:
A sample of matter consisting of identical particles could be an element, as elements are made up of only one type of atom with identical size, mass, and properties, forming a pure substance with a constant composition throughout the sample.
Step-by-step explanation:
If a sample of matter is made of identical particles, that sample could either be an element or an atom, but not a compound or a mixture. An element is composed of one type of atom throughout, meaning all atoms in that sample have the same size, mass, and other properties. Matter is anything that occupies space and has mass, and it is made up of atoms. Atoms are the smallest units of an element that retain all the properties of that element.
Elements and compounds are considered pure substances because they have a constant composition. Compounds are composed of more than one type of atom; hence the sample mentioned in the question cannot be a compound if it consists of identical particles. It also cannot be a mixture, as mixtures involve the physical combination of two or more different types of particles, either elements and/or compounds.